program factorial_iterative;
#include( "stdlib.hhf" )
// Phil Gardner
procedure factorial; @noframe; @nodisplay;
begin factorial;
cmp( ax, 0 );
// Can't deal with factorial of negative number
jl tooSmall;
// Zero or above can be displayed though
// Factorial of 0 is automatically 1
jz isZero;
// Any number larger than 1 requires working out
stdout.put( nl, "Calculating factorial of " )
stdout.puti16( ax );
stdout.put( " is " );
stdout.puti16( ax );
mov( ax, bx );
keepMultiplying:
dec( bx );
cmp( bx, 0 );
jz finishedFactorial;
mul( bx, ax );
stdout.put( " x " );
stdout.puti16( bx );
jmp keepMultiplying;
isZero:
stdout.put( nl, "Factorial of 0 is always 1" );
mov( 1, ax );
finishedFactorial:
stdout.put( nl, "Returning result ")
stdout.puti16( ax );
stdout.put( nl );
ret();
tooSmall:
stdout.put( nl, "Must be >= 0", nl );
ret();
end factorial;
// - - - - -
begin factorial_iterative;
mov( -1, cx );
keepCalculatingRange:
mov( cx, ax );
call factorial;
inc( cx );
cmp( cx, 6 );
jle keepCalculatingRange;
stdout.put( nl, "Finished.", nl );
end factorial_iterative;
